Generation and Persistence of CD4 Memory Subsets Recently we found that flu-specific CD4 T cell effectors provide protection against lethal challenge by virtue of both direct cytolytic activity (ThCTL) and help for Ab, suggesting additional functional heterogeneity among CD4 subsets that may contribute to CD4 memory heterogeneity and help us uncover new mechanisms of vaccine-induced protection. We have recent evidence that IL-17 producing CD4 also play a role in combating influenza. Our goal here is to evaluate the hypothesis that ThCTL cells represent a distinct functionally specialized subset that with Th1 and Th17 participate in an effective immune response. We will compare ThCTL to Th17 and Th1 subsets at the effector stage to further define their respective functions and determine how they provide protection in the lung against influenza. We will ask if ThCTL and Th17 give rise to committed memory subsets and determine their roles in combatting influenza. To accomplish these aims we will: 1) Isolate defined CD4 effector subsets generated in vitro and develop a scheme to separate them when they develop in vivo. We will define their cytokine and chemokine profiles, their migration and their involvement in help, cytotoxicity and protection against challenge with influenza. We will use the functional profile to develop a signature for each subset; 2) We will determine each subset's ability to give rise to memory cells that respond to challenge and develop into secondary effectors and ask if they retain the same functional potential as they progressively differentiate; and 3) We will evaluate the mechanisms used by each memory Th subset to provide protection against lethal flu challenge. We will collaborate with: 1) Project 2 to determine which how the CD4 subsets compare with parallel CDS effector and memory subsets; 2) Project 3 to determine migration of the CD4 subsets, and behavior in the lung and how interactions with selectins regulates function and memory generation from effectors; 3) Project 4 to investigate whether similar Tuberculosis Ag-speeific CD4 subsets can improve protection against Tuberculosis infection.